The present invention relates to a method for forming vertical stacks of documents, such as magazines or newspapers, from documents which are sequentially delivered to the apparatus, and for then conveying the stacks sequentially along a path of travel while maintaining the vertical alignment of the stacks.
Modern stack forming machines are able to rapidly form vertical stacks of documents from documents sequentially delivered thereto, and to eject the stacks horizontally onto a longitudinally extending driven conveyor by which the stacks are transported to further processing operations, such as binding and labeling stations. When such machines are run at high speed, the ejector must be cycled very rapidly, and the rapid ejection of the stacks tends to cause misalignment or shingling in the forward or longitudinal direction, as illustrated in FIG. 2 of the accompanying drawings. Also, the documents may slide laterally.
In an attempt to alleviate the shingling and alignment problems, it has been proposed to mount lugs or paddles on the conveyor which engage the leading end of each stack causing it to square up, and the lugs or paddles are then moved out of the way to permit the stack to continue its advance. This arrangement has not been totally satisfactory however since the movement of the lugs or paddles requires significant equipment and time, and thus production speeds are limited.
It is accordingly an object of the present invention to provide an apparatus for forming stacks of documents and ejecting the formed stacks onto a longitudinally extending conveyor at high production speeds, and which is able to correct and/or maintain the vertical alignment of the stacks as they are conveyed along the conveyor.
It is also an object of the present invention to provide an apparatus of the described type which squares the stacks in both the longitudinal and lateral directions.
The above and other objects and advantages of the present invention are achieved by the provision of a method which comprises the steps of forming a stack of documents, and ejecting the stack onto a longitudinally extending conveyor so that the stack moves longitudinally onto the conveyor at a predetermined speed. The opposite sides of the ejected stack are engaged by a pair of rotating guide rolls, and the guide rolls are rotated about their respective axes at a peripheral speed which closely approximates the predetermined speed of the stack. The rotational speed is then reduced so as to decelerate the stack.
The conveyor onto which the stacks are ejected is typically driven at a relatively slow speed which is set to correspond to the infeed speed of the downstream processing equipment. However, the stacks must be rapidly ejected onto the conveyor to achieve the desired production output, and thus the ejection speed is preferably above the delivery speed of the conveyor. To accommodate these differing requirements, a controller is provided which is operatively connected so as to control the rotational speed of each of the drive motors of the guide rolls such that during passage of each stack through the gate, the guide rolls have an initial peripheral speed which closely approximates the advancing speed of the stack, and the initial peripheral speed is reduced during the passage of the stack through the gate so as to decelerate the stack, preferably to the delivery speed of the conveyor. A sensor is provided for sensing the advancing speed of the stacks of documents as they move longitudinally along the conveyor toward the gate, and the controller is operatively connected to the sensor and to each of the drive motors of the guide rolls for controlling the initial rotational speed of each of the guide rolls as a function of the advancing speed of the stacks as the stacks advance toward the gate. The engagement of the stack is preferably designed to occur at, or a short time after, the time the ejecting mechanism has reached its full forward stroke. As a result, the engagement of the stack with the guide rolls acts to square the stack.
The conveyor preferably comprises a plurality of parallel conveyor rollers which define the support surface, a conveyor drive motor, and a friction drive transmission between the conveyor drive motor and the conveyor rollers whereby the conveyor rollers are rotatably driven by the conveyor drive motor so as to allow slippage therebetween. Thus the mismatched speeds of the stacks and the conveyor as the stacks move through the gate can be accommodated.